Fiber optic splitter

Fiber optic splitter, also named beam splitter. It is based on a quartz substrate of integrated waveguide optical power distribution device that is same as coaxial cable transmission system. The optical network system also needs to be an optical signal coupled to the branch distribution. In which requires the fiber optic splitter is one of the most important passive devices in the optical fiber link, is optical fiber tandem device with many input terminals and many output terminals, Especially applicable to a passive optical network (EPON, GPON, BPON, FTTX, FTTH etc.) to connect the MDF and the terminal equipment and to achieve the branching of the optical signal.

Fiber optic splitter is a key optical device in passive optical network (PON) systems, also known as a passive optical splitter, which splits the optical signal power evenly into all the output ports. In the PON field plant, a 1 × 8 to 1 × 32 splitter is placed on an electric pole, connecting the distribution optical cable in the air and the drop wire to the customer premises. A 1 × N splitter can be part of an N × N star coupler. ^[1]

For example, a 16 × 16 star coupler with four-stage topology is shown in the figure beside, and the dotted line denotes a 1 × 16 splitter. The star coupler can be constructed by cascading 3-dB couplers in the perfect shuffe topology. The 3-dB coupler has two input and two output ports, and it splits the input power 50:50 to the output ports. The number of 3-dB couplers required for the case with k-stage 1 × dBcoupler is given by: N_{3dB coupler} = 2^k - 1, k = log₂N and the splitting loss per output port is given by: Splitting loss = 3 k [dB] For a 1 × 16 splitter, k = 4, the number of 3-dB couplers required is 31, and the splitting loss per output port is 12 dB + splice Loss appr 0.3 dB per stage. 1 x 16 splitter is 12dB + 4 x 0.4 = 12+1.6 = 13.6dB

Higher order splitters can be constructed as k-stage arrays of such couplers. They have one or two input ports and N_{3dB coupler} = 2^k output ports, as shown in the figure below. The number of output ports is called the split ratio, which corresponds to the maximum number of ONUs that can be connected. ^[1]

Types

According to the principle, fiber optic splitters can be divided into FBT (Fused Biconical Taper) splitter and PLC (Planar Lightwave Circuit) splitter.

FBT splitter is made out of materials that are easily available, for example steel, fiber, hot dorm and others. All of these materials are low-price, which determines the low cost of the device itself. The technology of the device manufacturing is relatively simple, which has the impact on its price as well. In scenario where multiple splits are needed, the size of the device may become an issue. It is important to keep in mind that splitters are being deployed in the fields either in cabinets or in strand mountings, so the size of device plays a critical role. FBT splitters only support three wavelengths (850/1310/1550 nm) which makes these devices unable to operate on other wavelengths. Inability of adjusting wavelengths makes FBT splitters less customizable for different purposes. Moreover, the devices are to a high extent temperature sensitive, providing a stable working range of -5 to 75 °C. In certain areas, such as Scandinavian countries this temperature restrictions may be crucial. The signal processed by FBT splitters cannot be splitted evenly due to lack of management of the signals.

PLC splitter manufacturing technology is more complex. It uses semiconductor technology (lithography, etching, developer technology) production, hence it is more difficult to manufacture. Therefore, the price of the device is higher. However, there is a number of advantages the device possesses. The size of the device is compact, compared to FBT splitters, making it suitable for density applications. PLC splitter operates at wider temperature range (-40 to 85 °C), allowing its deploying in the areas of extreme climate. The split ratio goes up to 64, providing a high reliability. Furthermore, the signal can be split equally due to technology implemented. A range of wavelengths (1260 – 1650 nm) is provided, so the wavelengths are adjustable. Critical points of the device that might fail are input and output, so the general risk of failure is low.

Splitting Ratio Principle

FBT splitter makes two (two or more) fibers removed the coating layer gather in a certain way, stretched to both sides under the heating zone at the same time, form a double cone’s special waveguide structure finally for getting a different splitting ratio via controlling length of the fiber torsion angle and stretch.

PLC splitter is a micro-optical element using photolithographic techniques to form optical waveguide at medium or semiconductor substrate for realizing branch distribution function.

Technical Index

FBT splitter: Operating wavelength, Operating bandwidth, typical additional loss, insertion loss, polarization dependent loss, uniformity and directivity and splitting ratio
PLC splitter: Operating wavelength, insertion loss, uniformity, return loss and polarization dependent loss
Loss of splitter : Loss of spiltter is 3dB x k (no. of stage) + splice loss (.4 dB each stage)

Advantages and Disadvantages

Advantages

FBT splitter: low cost, raw materials procured easily (quartz substrate, stainless steel, fiber, hot dorm, GEL), splitting ratio according to the needs of real-time monitoring, can make unequal splitting ratio.
PLC splitter: Loss is not sensitive to the wavelength of the transmitted, to meet the transmission requirements of different wavelength, spectral uniformity, the average signal assigned to the user, compact structure, small volume, low cost of more points, the more obvious cost advantage.

Disadvantages

FBT splitter: Loss sensitive wavelength, the different wavelengths should be chosen different devices, the poor uniformity, can not ensure uniform spectroscopic, insertion loss changes large with temperature variation is greater.
PLC splitter: the device fabrication process complexity, high technical threshold.

References